Pressure vessel

ABSTRACT

A pressure vessel providing more efficient use of constituent material for containing fluid pressurized to a predetermined operating level, and being provided with infinite cycle life. The vessel may include an array of radially disposed segmented blocks supplied with compressional axial and tangential support forces such that when the contained pressurized fluid is pressurized to its operating level, the working stress across the array of segmented blocks does not exceed the fatigue or endurance stress of the material of which the blocks are made, and/or the vessel may include a multiring assembly wherein the radial interferences between adjacent rings are chosen such that at each radius except the outermost, the working stresses are made substantially equal to each other and made equal to, or below, the fatigue or endurance stress of the material of which the rings are made.

nite States Patent [151 ,3,16 Wenltatesan 1 Jan, 1, 119m [54] PRESSURE VESSEL 3,490,344 1/1970 Archer et a1 ..92/171 [72] Inventor: Peruvemba Swaminatlian Venkatesan,

Norrisville, Pa.

Primary Examiner-Robert L. Spicer, Jr. Attorney-W. M. Kain, R. P. Miller and R. C. Winter [73] Assignee: Western Electric Company, Incorporated,

New York, N.Y. [57] ABSTRACT Filed? P 18, 1969 A pressure vessel providing more efficient use of constituent [21] APPL NO; 858,970 material for containing fluid pressurized to a predetermined operating level, and being provided with infinite cycle life. The vessel may include an array of radially disposed seg- [52] 1.1.8. Cl ..425/77, 92/171, 100/269, memed blocks supplied with compressional axial and mugs. 100/295, 264/314, 425/4 tial support forces such that when the contained pressurized [51] Ill. C1 ..B29C 3/00, 1330b l/32 fluid is pressurized to i operating level, the working Stress [58] Field ofSearch ..100/269,295; 18/16.5, 16R, across the array of Segmented blocks does not exceed the 18/34 35; 264/314; 25/128 D; fatigue or endurance stress of the material of which the blocks 92/l69 192/88 85 AT are made, and/or the vessel may include a multiring assembly 56 R t d wherein the radial interferences between adjacent rings are 1 e erences chosen such that at each radius except the outermost, the UNITED STATES PATENTS working stresses are made substantially equal to each other and made equal to, or below, the fatigue or endurance stress 2,554,499 5/1951 Poulter 1 8/34 R fth material f hi h the rings are made. 3,224,042 12/1965 Meissner .100/269 R X 3,379,043 4/1968 Fuchs, Jr. ..18/16 R X 28 Claims, 5 Drawing Figures PATENYEU JAN 1 8 m2 SHEET 3 BF 4 rnrssurs VESSEL BACKGROUND 1. Field of the Invention This invention relates to pressure vessels for containing pressurized fluids, in particular, highly pressurized fluids; and more particularly, to pressure vessels for containing fluids which are pressurized and depressurized repeatedly, or infinitely (infinitely in the sense that the crank shaft of an automobile is designed to have infinite cycle life). Further, this invention is directed toward providing a pressure vessel which makes a more efficient use of the constituent material for containing fluid pressurized to a given level, and in addition, this invention relates to pressure vessels for containing fluids which are pressurized to levels which are in excess of the fatigue or endurance stress of the strongest generally commercially available materials, i.e., not specialty materials.

2. Description of the Prior Art Known to the prior art are many types of pressure vessels for containing a pressurized fluid in a central chamber. Some prior art vessels include an array of radially disposed, segmented blocks which provide radial support to the central chamber when the fluid contained thereby is pressurized to its operating level. Other prior art pressure vessels include the socalled multiring, or shrunk-ring, assembly wherein interferences between adjacent rings are such that the assembly is generally prestressed radially inwardly when the contained fluid is depressurized, so as to provide the multiring assembly with greater pressurized fluid containing capacity when loaded.

With specific regard to the prior art pressure vessel includ ing an array of radially disposed, segmented blocks, such blocks are segmented to prevent the generation of unwanted or ruinous tangential stresses when the fluid contained therein is pressurized to its predetermined operating level. Also known is the technique of enhancing the pressure containing capacity of such a pressure vessel by providing radial support stress to the segmented blocks such that when the contained fluid is pressurized to its predetermined operating level, the radial stress experienced by the blocks is maintained within tolerable limits. Such radial support stress is typically provided by a surrounding concentric body of pressurized support fluid.

With specific regard to prior art multiring pressure vessels, the typical approach for enhancing the pressure containing capacity of a multiring pressure vessel has been to give attention to the tangential stress in the rings when the fluid contained thereby is pressurized to its operating level. More specifically, radial interference between rings has been provided to reduce the tangential stress present in the rings when the contained fluid is pressurized, from that value which would be present in a pressure vessel made of monolithic block, the contained fluid being similarly pressurized. Such prior art radial interferences are usually determined empirically, however, radial interference equations are available in the prior art for a two-ring pressure vessel whereby the tangential stress at the bore of the vessel can be maintained at or below a chosen value. For pressure vessels of more than two rings, such equations are not available and it has been found that the prior art pressure vessels of more than two rings have random, or even haphazard, tangential stress patterns across the constituent rings, depending upon the actual radial interferences present between the rings.

There are two primary operational considerations with regard to any pressure vessel, (1) the level to which the fluid contained by the vessel can be safely pressurized without fear of rupture, i.e., the upper pressure operating limit; and (2) the number of times the fluid contained by the vessel can be pressurized to the upper operating limit, and depressurized, before the pressure vessel fails from material fatigue, i.e., the cycle life of the vessel.

The aforementioned prior art pressure vessels generally satisfy both operational considerations while operation at the lower pressure levels (e.g., below 150,000 p.s.i.); and, as is LII known, by the use of highly excessive specialty materials and/or expensive and complex structural arrangements, such vessels can be designed to contain pressures up to, and in excess of, 500,000 p.s.i. However, in containing such elevated pressures, the vessels either have an extremely short cycle life (typically 10 cycles or less) which renders them commercially infeasible, or the vessels are inetficient in that they are so expensive, complex or massive vis-a-vis the commercial end to be achieved, that they are not commercially feasible.

With regard to cycle life, this consideration is quite highlighted by the fact that the strongest material presently commercially available (i.e., not specialty materials), for example a maraging steel, has a fatigue stress, or endurance stress, of only about 150,000 p.s.i. This means that a prior art pressure vessel as described above, constructed of maraging steel, could certainly not be safely operated above, or even slightly below, 150,000 p.s.i. without paying the price of an undesirably abbreviated cycle life. This limitation, obviously, places a commercial ceiling on the applications wherein pressurized fluid levels above 150,000 p.s.i. are required, or found to be highly desirable, for material forming or shaping; and more importantly, such limitation precludes such prior art pressure vessels from having an infinite cycle life (as noted above, infinite cycle life in the sense that the crankshaft of an automobile is designed to have infinite cycle life).

Accordingly, there exists in the pressure vessel art a need for a pressure vessel which makes a more efficient use of constituent material, and which can, with commercial feasibility, contain a pressurized working fluid which is pressurized to a lever which is in excess of the fatigue or endurance stress of the material of which the pressure vessel is made. There further exists a need for pressure vessels which have infinite cycle life in the sense noted above.

SUMMARY The primary thrust of the present invention is directed toward providing a pressure vessel for containing fluids, in particular highly pressurized fluids, which has an infinite cycle life (as noted above) of pressurization and depressurization. Additionally, the present invention is directed toward providing a pressure vessel which makes a more efficient use of the constituent material for containing fluid pressurized to a given level. Further, the invention is related to a pressure vessel for containing pressurized fluids with generally commercially available materials whose fatigue or endurance stress is less than the pressure level to which the fluids contained therein are pressurized.

Referring now specifically to pressure vessel material infinite cycle life, it has been found that the cogent criterion is not any individual stress experienced by such material, i.e., the radial stress 8,, or the axial stress S,,, or the tangential (hoop) stress 5,, but rather the combined effect of these stresses, which was defined by Von Mise as the working stress" 8,, and expressed as follows:

w 1| r) r t) t n) The working stress 5,, was equated to the yield strength by Von Mise, and generally is always so treated; however, in accordance with the teaching of the present invention, by equating the working stress 8,, to the fatigue or endurance stress S, of the material of which the pressure vessel is made, and by employing the material in accordance with the present invention such that Von Mises equation is satisfied when the vessel is loaded to its predetermined operating level, the pressure vessel is provided with infinite cycle life, and the vessel can, with safety and commercial feasibility, contain fluid pressurized to a level in excess of the fatigue or endurance stress of the material of which the vessel is made.

The above-noted prior art problems are overcome by a pressure vessel embodying the present invention, which pressure vessel may include an array of radially disposed segmented blocks which are supplied with. compressional axial and tangential support forces such that when the pressurized fluid contained thereby is pressurized to its predetermined operating level, the working stress across the array of segmented blocks does not exceed the fatigue or endurance stress of the material of which the blocks are made. Additionally, such prior art problems are overcome by a pressure vessel embodying the present invention which may include a multiring assembly wherein the interferences between adjacent rings are chosen such that at each radius except the outermost, the working stresses are made substantially equal to each other, and also made substantially equal to or below the fatigue or endurance of the material of which the rings are made.

The primary advantages of pressure vessels embodying the present invention are that such pressure vessels provide a more efficient use of constituent material for containing fluid pressurized to a given level, and such vessels are provided with infinite cycle life. Further, the present invention permits pressure vessels to be made of commercially available materials having a fatigue or endurance stress which is less than the pressure level to which the fluid to be contained by the pressure vessel is to be pressurized.

FIG, 1 is a cross-sectional view of a pressure vessel embodying the present invention;

FIG. 2 is a cross-sectional view taken along the line 22 in FIG. 1;

FIGS. 3 and 4 are diagrammatic views illustrating one aspect of the present invention relating to an array of radially disposed segmented blocks; and

FIG. 5 is a tabulation of calculations of an example of one aspect of the present invention relating to a multiring assembly.

GENERAL FIGS. 1 and 2 show diagrammatically a pressure vessel embodying the present invention. The pressure vessel includes an inner array of radially disposed segmented blocks 12 embodying the present invention and for supporting a body of pressurized operating fluid 11, an intermediate cylindrical jacket of support fluid 14, and an assembly of multirings l6 embodying the present invention for containing the support fluid 14 or an operating fluid such as fluid 11. The operating fluid 11 is contained in a centrally provided chamber 17, and the support fluid 14 is contained in an annular chamber 18 concentrically surrounding the array of segmented blocks 12.

The pressure vessel is provided with end members 20 and 22 suitably constructed so as to accommodate and contain annular bodies of support fluid 24 and 26 respectively. Support fluids 24 and 26 pressure bias annular pistonlike members 28 and 30, respectively, for providing inwardly directed, compressive axial support to the segmented blocks 12, in a manner to be described more fully below. The end members 20 and 22 are suitably bored to slidingly accommodate opposed top and bottom pistons 32 and 34, which pistons may be driven to pressurize the operating fluid ll residing within the centrally provided pressure chamber 17. Also residing within the pressure chamber 17, in the manner known in the art, is a seal support cylinder 40 for maintaining suitable fluid seals S shown surrounding the pistons 32 and 34 in their appropriate sealing positions. Further, in the manner known in the art, the pressure vessel 10 is provided with suitable liners L, positioned on each side of the array of segmented blocks 12, for preventing passage of pressurized fluid between the segmented blocks.

In general, the array of radially disposed segmented blocks 12 are supplied with compressional axial support stress from the members 28 and 30, and with compressional tangential support stress or forces from the support fluid 14 such that when the operating fluid 11 is pressurized to its operating level, the working stress 8,, across or experienced by the segmented blocks does not exceed, or substantially exceed, the fatigue or endurance stress S, of the material of which the blocks are made; thus, the operating fluid 11 may be repeatedly pressurized and depressurized without the working stress across the array of segmented blocks 12 substantially exceeding the fatigue stress of the material of which the blocks are made, and hence, the array of segmented blocks is provided with infinite cycle life. Further generally, the interferences between adjacent component rings of the multiring assembly 16 are chosen such that, when the fluid supported thereby is pressurized to its predetermined operating level, (i) the working stress S across each ring does not exceed the fatigue or endurance stress S, of the material of which the multirings are made, thus providing the multiring assembly with infinite cycle life, and such that (ii) the working stress S m at the interfaces between the rings (or at the radii R3, R and R4 of FIG. 2) are equal or at least substantially equal, thus providing a more efficient use of the multiring constituent material.

ARRAY OF SEGMENTED BLOCKS The array of segmented blocks 12 of FIGS. 1 and 2 is segmented to eliminate the generation of tensional tangential stress which, vis-a-vis the material of which the blocks may be made, can quickly become ruinous, particularly if it is desired to contain an operating pressure P, in the order of 300,000 p.s.i., and the blocks are made of generally commercially available materials.

As mentioned above, the strongest" commercially available materials, e.g., a maraging steel, has a fatigue or endurance stress S, of about 150,000 p.s.i. and it will be assumed that the blocks 12 are made of material having a fatigue or endurance stress of 150,000 p.s.i. Further, it will be assumed that the operating fluid 1 l is pressurized to an operating pressure P, of 300,000 p.s.i. The support fluid 14 will be pressurized to a pressure level P, which will be arbitrarily assumed or chosen to be 100,000 p.s.i., for purposes of illustration. However, it will be understood that the pressure level P, may be of other values in accordance with the present invention.

Accordingly, as noted above and on the basis of the foregoing assumed conditions, if the array 12 is to have infinite cycle life, the working stress 8,, at each point across the array must not exceed, or substantially exceed, 150,000 p.s.i. the assumed fatigue or endurance stress S; of the material of which the blocks 12 are made, when the fluid supported thereby is pressurized to its predetermined operating level.

Superimposed on the right-hand portion of the array 12 in FIG. 3 is a plot of radial stress S, vs. the radial length L, of a representative segmented block 44 of the array 12, the radial stress S, being the radial stress experienced by the block 44 when the operating fluid 11 is pressurized to the assumed operating level I" of 300,000 p.s.i., and the support fluid 14 is pressurized to the assumed level of 100,000 p.s.i. (It will be understood at this juncture, i.e., with no support stresses or forces yet applied, that the working stress S,,. is equal to the radial stress S, at each point across the radial length L, since the array of blocks 12 are only experiencing radial stress. Hence, the plot in FIG. 3 is also a plot of working stress 8,, vs. the length L,.) Thus, as shown, it will be noted that the radial stress S, and the working stress 5,, across the radial length L, of the block segment 44 will drop from approximately 300,000 p.s.i. at the bore D, of the pressure chamber 38, to 100,000 p.s.i. at diameter D l00,000 p.s.i. being the assumed value of the support fluid pressure P,.

Since the support fluid P, of 100,000 p.s.i. is less than the allowable working stress S,,, of l50,000 p.s.i. of the material of the block 44, the radial stress S, and working stress S across the radial length L, of the block 44 will drop to the value of the allowable working stress 8,, at some diameter D which will be, as shown, intermediate the bore or chamber 17 diameter D, and the fluid support jacket diameter D It will be appreciated that between diameter D,,, and diameter D represented by trapezoidal cross-hatched area A the radial stress S, and working stress S are less than the allowable working stress of 150,000 p.s.i., and hence attention need not be given to this area. However, for infinite cycle life, the working stress in excess of 150,000 p.s.i. between the chamber diameter D, and the diameter D (represented by triangular cross-hatched area A,) must be reduced and made substantially equal to, or less than, the allowable working stress 8,, of 150,000 p.s.i.

It has been discovered that this reduction in working stress can be accomplished by the application to each block segment 4d of compressional axial support stress S and compressional tangential support stress 8,, as shown diagrammatically in FIG. 4, which will vary from (P,,-S,,,) at the chamber diameter D,, to zero (0) at the diameter D,,,; it being understood that the hoop stress can be ignored due to the blocks 12 being segmented. By setting the compressional axial and tangential support stresses to be supplied equal to each other to eliminate the presence of two unknowns in one equation (and by assigning to each the common mathematical symbolic notation 8,), Von Mises equation, equation (1) supra, can be written for the block segment material at the bore of the pressure chamber, i.e., at diameter D,, and the value of the axial and tangential support stresses S, at the diameter D, necessary to satisfy Von Mises equation at diameter D, can be solved. Such equation can be shown to be:

o c) w c 0 w) Since, in accordance with the teaching of the present invention, 5,, is set equal to the endurance or fatigue stress of the material of the block segment 44, equation (3) can be rewritten as:

c n f) Further, since both the assumed values of the operating fluid ll (300,000 psi.) and the working stress 8,, (150,000 p.s.i.) are known, the value of compressional axial and tangential support stresses S which must be supplied at diameter D, in order to reduce the working stress 5,, in each block segment at the diameter D, to the endurance or fatigue stress S, of the material of the block 44, can be determined.

In terms of specific apparatus, the axial compressive support stress S or S required will be provided by the pistonlike members 20 and 30 shown in FIG. ll. The tangential compressive support stress S, or S required will be provided by the support fluid 14, shown in FIGS. 1 and 2.

Thus, it will be understood that the support fluid M must provide two quantities, viz, l radially inwardly directed radial force for countering the radially outwardly directed radial force from operating pressure 11 (FIGS. 1 and 2), i.e., the counterforce for maintaining the segmented block array 12 in equilibrium, and (2) radially inwardly directed stress or force for wedging or compressing the segmented blocks together with sufficient compressive stress so as to apply compressional tangential support stress S, or S thereto which assists the compressional axial support stress 5,, or S (supplied by pistons 32 and 34) in reducing the working stress S between diameters D, and D to substantially the value of the endurance or fatigue stress 8,, of the block material thereby satisfying Von Mises equation at each point between such diameters and thus providing the array of segmented blocks ll2 with infinite cycle life.

Further, it will be appreciated from FIG. 3 that the perfectly required axial and tangential compressive support stresses S required to be supplied would be varying stresses. It is difficult, however, to provide a varying stress in actual practice; accordingly, an average compressional support stress 8,, or t on: or c am: of:

will be used to determine the diameter D,,; the determination of diameter 0,, being an intermediate determination permitting the determination of diameter D the outer diameter of the array 12. It will be understood by those skilled in the art that the use of an average support stress is a compromise for which at least some price must be paid with regard to the perfect attainment of infinite cycle life. However, even with the use of an average support stress, infinite cycle life is substantially obtained.

Accordingly, the value of diameter D,,, can be determined as follows: diameter D,,, will be that diameter which will provide an area, which area when multiplied by the allowable working stress 8,, (or the fatigue or endurance: stress of the material of the segmented blocks l2) will provide the radially inwardly directed force for (l) maintaining the array of blocks 12 in equilibrium, and (2) for supplying the average compressional tangential support stress S, or S for assisting in reducing the working stress between diameters D, and D to substantially the value of the allowable working stress 5,, for infinite cycle life. Such equation can be shown to be:

By again setting the operating pressure P, equal to the assumed value of 300,000 p.s.i., and by setting the working stress 8,, equal to the assumed value of 150,000 p.s.i., the assumed value of the fatigue or endurance stress of the block material, and since D, is known (such diameter being the operating chamber 17 required for a given workpiece shaping operation), the diameter D, can be determined. Once diameter D has been determined, the diameter D, can be determined as follows: diameter D will be that diameter which will provide an area, which area when multiplied by the support fluid pressure P,(arbitrarily and conveniently chosen above as 100,000 psi.) will provide the radially inwardly directed force for (l) maintaining the array of segmented blocks 12 in equilibrium, and (2) for supplying the average compressive tangential support stress .5, or S, m for assisting in providing the reduced working stress S between the diameters D, and D for infinite cycle life, as taught above. Thus, by writing the radial force balance ro equilibrium equation between diameters D, and D and providing such twofold radially inwardly directed force or stress, the diameter D, can be determined. Such equation can be shown to be:

w l o'" w/ 1= r 2 (1) Since in view of the foregoing assumptions and computations, the only unknown now is diameter D diameter D, can be determined.

Accordingly, it will be understood that the pistons 20 and 30 will be structured in the manner so as to provide the array of segmented blocks 12 with the average compressional axial support stress 8,, or S, am over the area between diameters D, and D,,,; and the support fluid M, the array being structured so as to be provided with diameter D as determined above, will provide the array of segmented blocks 12 with the average tangential compressive support stress S, or S, Thus, when the fluid 1111 is pressurized to its operating level, the actual working stress S across the array of segmented blocks 12 between diameters D, and D,,, will be substantially reduced to the value of the fatigue or endurance stress of the material of which the array of blocks 112 are made, and hence at no point across the array will the working stress substantially exceed the fatigue or endurance stress of the material of which the blocks i2 are made. Accordingly, the array 12 will be substantially provided with infinite cycle life.

As noted above, in the development of the foregoing equa tions, the fatigue or endurance stress S, of the material of the blocks 12 was substituted directly for the allowable working stress 8,, and hence the average compressional support stresses S were developed so as to reduce the working stress between diameters D, and D,,, to substantially the value of the material fatigue or endurance stress. It will be understood that such working stress could be further reduced, or made any predetermined ratio of, the allowable working stress by substituting the term KS; (instead of simply S for the term S,,,, where K is a fraction or number greater than unity. By such substitution, the working stress 8,, can be made to be any predetermined ratio, i.e., fraction or multiple, of the fatigue or endurance stress of the material of which the blocks M. are made.

Referring again to H6. ll, support lluid ll ll is supplied from a source (not shown) to the annular chamber 1% through a passageway 42 formed longitudinally in a block of the segmented array 112, and through a dependent pipe portion 44 formed integrally with the segmented block. This manner of supplying the pressurized support fluid 14 set forth in detail in a copending patent application of the assignee of the present invention, Ser. No. 652,1 l2, filed July 10, 1967, now US. Pat. No. 3,490,344, in the names of John W. Archer and F. J. Fuchs, .lr.

With further reference to P10. 1, while the use of two pistonlike members 28 and 30 is particularly useful in supplying the compressional axial support stress S, in accordance with the teaching of the present invention, such axial support stress may be provided by a single pistonlike member, such as pistonlike member 28, and the complementary support stress may be provided by reactive forces from a monolithic block which would replace block 22 including the pistonlike member 30.

MULTIRING ASSEMBLY A. Bore Pressurized Referring now to the present invention as embodied in the multiring assembly 16 of FIGS. 1 and 2, the assembly is subjected to the internal pressure P, of the pressurized support fluid 14 (or as noted above, the multiring assembly could be utilized to directly support an operating fluid such as fluid l l As is known in the art, for a constant or uniform working stress 8,, across the rings of a multiring pressure vessel, the rings would be of an infinite number with each ring being of an infinitesimally small thickness. Obviously, practical considerations negate such an approach. In accordance with the present invention, the ideal is approached, inter alia, by use of a design criterion 1+X where X is a dimensionless number which will be treated in detail infra. The design criterion 1+X is a variable design criterion and, except for the last or outermost ring, is made equal to the ratio of the outside radius to the inside radius of each ring in the assembly, viz:

Use of this design criterion makes it possible to relatively determine the radii of any ring in an assembly except the outside radius R,, as set forth below:

1ll l+X)" 2R1 it will be understood that the radius R, will be known, such dimension being determined typically by the diameter of the fluid chamber supported by the multiring assembly such as central chamber 17 or annular chamber 18. Hence, once X is chosen all radii except the outermost will be known. And it will be understood by those skilled in the art that with regard to multiring assemblies comprised of tapered rings which are press fitted together, such radii are midpoint radii with regard to ring height of such tapered rings.

For the optimum pressure vessel design, i.e., the most efficient use of the material of which the rings are made, the working stresses S at radii R,, R ,...R,, when the contained fluid is pressurized to its operating level, are required to be equal or substantially equal; and for infinite cycle life as noted above, the working stress S across each ring must not exceed the fatigue or endurance stress S, of the material of which the rings are made. With the multiring assembly 16 of FIG. 2 subjected to the internal pressure P,, and since no axial stress S is applied to the assembly 16, the only stresses present at radii R,, R,,...R,, are the radial compressive stresses 8,, and the tangential, tensile stresses 8,. For a known or desired working stress 8,, and a known internal or bore pressure P,, the tangential stress 8,, acting at radius R, can be obtained by solving the following quadratic equation obtained from equation (1) above, viz:

since S,,,=P,, i.e., the radial stress at R, is equal to the pressure of fluid 14 or P,, equation (9) can be rewritten as:

w rr i+( -ri' i) l0) For a known ring material, S,,, will be known being made equal, as above, to the fatigue or endurance stress S, of the material of which the rings 16 are made; and P, will be known being the pressure of the support fluid 14, now assumed to be, for example, 150,000 p.s.i. Substitution of the knowns S and P, into equation (9) will give the tangential stress S acting at radius R, in terms of a quadratic equation. Solution of the quadratic equation will give S in terms of two roots, one value will yield a compressive tangential stress and the other value will yield a tensile tangential stress including the value zero. The latter root is chosen over the former root because it represents a lower ring interference at radius R, and a lower maximum in tangential stress (typically compressive) at radius R, when the pressure P, is removed. Once the tangential stress 8,, is determined, the value of the radial compressive stress S acting at radius R,, provided by the outer rings and the pressure P, in order that the working stress at radius R, be equal to or substantially equal to the allowable working stress S (i.e., equal to S is obtained by use of the following equation:

Since P, is known (assumed or chosen value), since 8,, is known from equation (9), since radius R, will be known as noted above, and since R is known in terms of R, due to the design criterion (l+X), the only unknown is S which can be determined.

It will be noted from above that radial stress S is the sum of the radial stress at radius R, due to fluid pressure P, and that due to the total interference present at R after the entire multiring l6 assembly is assembled. Using the foregoing teaching with regard to the determination of tangential stress 8,, and radial stress S the tangential stresses S to S acting at radii R to R,, and the radial stresses S to S,,,,-,, may be determined; it being understood that such determination will be discontinued upon the radial stress 8,, equaling zero or upon its sign becoming negative. Since the exterior of the outer ring is exposed to the atmosphere, the radial stress at radius R, will be zero, thus, the outside radius R, of the last ring may then be determined from the following equation STE-'1 Ru2 R l which may be rewritten as: 7 l

R 2: S n-iRi+ Tn-l ?|-1 n 'ru-i lim-1 (1 The tables of FIG. 5 list values of the radii R, ...R,, (in inches) and the radial and tangential stresses (in p.s.i.) acting at radii R, to R,, when the supported fluid pressure P, (and hence S =l 50,000 p.s.i., X=0.4 and S,,,=150,000 p.s.i.

B. Bore Depressurized The ring interferences necessary at the various radii in order to have the working stresses S at the various radii, except the last, equal to each other and equal to, or substantially equal to the fatigue or endurance stress S of the ring material when the supported fluid P, is pressurized (e.g., fluids 11 or 14), are obtained by first determining the no-load radial stresses present at the various radii when the supported fluid P, is depressurized, i.e., the radial stress at the various radii due only to the ring interferences, for example, the radii stress present (with the supported fluid P,depressurized) at a particular radius due to the interference at the particular radius plus the radial stress at the particular radius due to the interferences present at any outer radii. The no-load radial stresses are obtained by subtracting the radial stresses acting at R,, R,,...R,, due to the supported fluid P, when pressurized, from the above-determined total radial stress present at these radii due to both the pressurized fluid P, and the total ring interferences As will be seen infra, the no-load radial stress will be utilized to determine the actual interferences at the radii.

While not required to determine the physical characteristics of the rings, it is desirable to determine the tangential stresses present in the rings when the supported fluid P is depressurized in order that the suitability of a given material for pressure vessel fabrication in accordance with the present invention may be more fully evaluated.

The no-load tangential stresses may be obtained as follows:

The actual interferences between rings are determined from what is termed in accordance with the present invention, the interference radial stresses. The interference radial stresses acting at R R and R are denoted by S S and S, respectively, and S for example, is defined as the interference radial stress acting at radius R after the first two rings are assembled, i.e., the radial stress acting at radius R due solely to the interference between the first two rings. More generally, the interference radial stress at particular inner radius is obtained by subtracting from the no-load radial stress at the particular inner radius, the component of the noload radial stress at the next adjacent outer radius acting back at the inner radius. More specifically, and by way of example, the interference radial stress S mm at radius R is obtained by subtracting from the above-determined no-load radial stress (S at radius R the component of the no-load radial stress (S no load) at radius R, acting at radius R i.e.,

SR3 no me 3 S no 0 R 2 Sim inmr= R 1w isp 4 R3 and so similarly for S, The interference radial stresses for radii R- R, are tabulated in FIG. 5, and such stresses in accordance with the present invention are converted into actual Dell/8,2

Delta (17) where E is the elastic modulus of the material of which the rings are made, and Deltan denotes the radial interference at R,, after n-2 rings are assembled. Referring again to FIG. E, there is shown a tabulation of actual ring interferences or Deltas (in inches) at radii R R and! R where, as noted above, P =l 50,000 p.s.i., X=0.4 and 5,, or S l 50,000 p.s.i.

With regard to the design criterion (H-X), X may be any value, however, it will be appreciated that as X decreases, the number of rings in the assembly will increase thereby causing an increase in manufacturing costs. Thus, it will be appreciated that for a given set of other conditions, an optimized value of X may be chosen so as to reasonably limit the number of rings to a reasonable minimum overall vessel size. it has been found that for multiring assemblies for supporting fluid pressures between 70,000 p.s.i. and 150,000 p.s.i., values ofX between 0.2 and 1.0 are particularly advantageous and useful.

As noted above, in the development of the immediately foregoing equations, the fatigue or endurance stress S, of the material of which the rings of the assembly 116 are made, was substituted directly for the allowable working stress S and hence the actual ring interferences or Deltas were developed so as to reduce the working stresses at the inner radii to the value of, or substantially the value of, the material fatigue or endurance stress, and hence equal to each other. It will be understood, as with regard to the array of segmented blocks M, such working stress could be further reduced, or made any predetermined ratio of, the allowable working stress by substituting the term KS, (instead of simply S for the term S,,,, where K is a fraction or number greater than unity. By such substitution, the working stress S 5,, can be made to be any predetermined ratio, i.e., fraction or multiple, of the fatigue or endurance stress of the material of which the rings of the assembly 16 are made.

With further regard to the radial interferences or Deltas, once such radial interferences are known and with the radii R, ...R,,, being determined as taught above, the rings of the multiring assembly may then be suitably constructed and assembled by being press fitted or shrunk fitted together in the manner known in the art.

Referring again to FIG. 2, there is shown, superimposed on the multiring assembly, a graph of the working stress 5,, across the rings of the assembly when the fluid M is pressurized to its predetermined level and the multiring assembly 116 has been constructed in accordance with the teaching of the present in vention. In the graph shown, it will be noted that the working stresses at all inner radii are equal, or substantially equal to, the fatigue stress S, of the material of which the rings are made. The working stress 5,, drops slightly across each inner ring and then drops slightly further across the other rings, however, the average of the graph would be a substantially uniform or constant working stress across the multiring assembly for increased efficiency of use of ring material.

Additionally, it will be understood from the foregoing, that the height of the segmented blocks l2 and rings of the assembly 116 is immaterial to the teaching of the present invention. Further, that such height may be of any reasonable value.

PRESSURE VESSEL lFllGS. l and 2 In summary, the pressure vessel 110, combining the abovedescribed array of segmented blocks l2 and the multiring assembly 116, provides a more efficient use of the material of which the segmented blocks and rings are made, and with commercial feasibility, permits the vessel to contain fluids pressurized to levels which are in excess of the fatigue or endurance stress of the strongest generally commercially available materials. Further, the working stress S,,, across the entire vessel, when the fluids 11 and 14 are pressurized to their predetermined levels, can be made equal to, or substantially equal to the fatigue or endurance stress of the material of which the segmented blocks and rings are made; or more generally, the working stress S can be made a predetermined ratio of such fatigue or endurance stress.

With regard to the term multiring assembly, it will be understood that such term in the foregoing specification and following claims defines an assembly including two or more rings.

Many modifications and variations of the present invention are possible in the light of the above teachings. it is therefore to be understood that the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A pressure vessel for containing a fluid to be pressurized to a predetermined level, comprising:

an array of radially disposed segmented blocks for supporting said fluid; and

means for supplying compressional axial and tangential support stresses to said array such that when said fluid is pressurized to said predetermined level the working stress across at least a portion of said array is a predetermined ratio of the fatigue stress of the material of which said blocks are made.

2. A pressure vessel according to claim 1 wherein said predetermined ratio is such that said working stress is substantially equal to the fatigue stress of the material of which said blocks are made.

3. A pressure vessel according to claim 1 wherein said predetermined ratio is such that said working stress is less than the fatigue stress of the material of which said segmented blocks are made.

4. A pressure vessel for containing a fluid to be pressurized to a predetermined level, comprising:

an array of radially disposed segmented blocks for supporting said fluid;

means for supplying compressional axial support stress to said array; and

means for supplying compressional tangential support stress to said array, said applied support stresses being of predetermined values such that when said fluid is pressurized to said predetermined level, the working stress across said array does not exceed the fatigue stress of the material of which said blocks are made.

5. A pressure vessel for containing a fluid to be pressurized to a predetermined operating level, comprising:

an array of radially disposed segmented blocks for supporting said fluid and which experience working stress upon said fluid being pressurized to said predetermined operating level;

means for applying compressional axial support stress to said array; and

means for applying compressional tangential support stress to said array, said support stresses being of predetermined values for making said working stress across at least a portion of said array a predetermined ratio of the fatigue stress of the material of which said segmented blocks are made.

6. A pressure vessel according to claim 5 wherein said predetermined ratio is substantially equal to the fatigue stress of the material of which said segmented blocks are made.

7. A pressure vessel according to claim 5 wherein said predetermined ratio is such that said working stress is less than the fatigue stress of the material of which said segmented blocks are made.

8. A pressure vessel according to claim 5 wherein said compressional axial support stress is provided by opposed pistons engageable with at least a portion of said array.

9. A pressure vessel according to claim 5 wherein said compressional tangential support stress is provided by a body of pressurized support fluid to be contained in an annular pressure chamber concentrically surrounding said array.

10. A pressure vessel according to claim 5 wherein said array is surrounded by a chamber for receiving a body of pressurized support fluid for providing said compressional tangential support stress.

11. In a pressure vessel including a central chamber for containing a body of operating fluid to be pressurized to a predetermined operating level P, the improvement comprising:

an array of radially disposed segmented blocks surrounding and supporting the chamber, said blocks experiencing working stress 8,, upon said operating fluid being pressurized to said operating level P, and

means for supplying compressional axial S, and tangential S,

support stresses to said array such that when said operating fluid is pressurized to said predetermined operating level P the working stress 8,, across at least a portion of said array is a predetermined ratio of the fatigue stress of the material of which said segmented blocks are made.

12. in a pressure vessel the combination according to claim 11 wherein said compressional axial S and tangential S, support stresses at the bore of said central chamber are substantially equal to the operating fluid pressure P, of said operating fluid minus the fatigue stress S, of the material of which said segmented blocks are made.

13. In a pressure vessel the combination according to claim 11 wherein said compressional axial and tangential support stresses applied to said array are average compressional support stresses substantially equal to [(D D,) (P,,-S,,,/2)].

14. A pressure vessel for containing a body of fluid to be pressurized to a predetermined level; comprising:

a multiring assembly including a plurality of rings for supporting said fluid,

said rings being provided with radial interferences such that when said fluid is pressurized to said predetermined level the working stress at each radius, except the outermost, is a predetermined ratio of the fatigue stress of the material of which the rings are made.

15. A pressure vessel according to claim 14 wherein said predetermined ratio is such that said working stress is equal to the fatigue stress of the material of which said rings are made.

16. A pressure vessel according to claim 14 wherein said predetermined ratio is such that said working stress is less than the fatigue stress of the material of which rings are made.

17. A pressure vessel for containing a body of fluid to be pressurized to a predetermined level, comprising:

a multiring assembly including a plurality of rings for supporting said fluid;

said rings fitted together and having radial interferences at the inner radii thereof; and

said interferences being such that, when said fluid is pres surized to said predetermined level, said radial interferences are such that the working stress at said inner radii are equal to each other and equal to the fatigue stress of the material of which said rings are made.

18. A pressure vessel for containing a body of fluid to be pressurized to a predetermined level, comprising:

a multiring assembly including a plurality of rings for supporting said fluid;

said rings being press fitted together and having radial interferences at the inner radii thereof; and

said interferences being such that, when said fluid is pressurized to said predetermined level, said stress at said inner radii are substantially equal to each other and less than the fatigue stress of the material of which said rings are made.

19. A pressure vessel for containing a body of fluid to be pressurized to a predetermined level, comprising:

a multiring assembly including a plurality of rings for supporting said fluid;

said rings being press fitted together and having radial interferences at the inner radii thereof; and

said interferences being such that when said fluid is pressurized to said predetermined level, the stresses experienced by said assembly at said inner radii are defined by:

a ap-l interf ii 1 (w 20. A pressure vessel, comprising:

an array of radially disposed segmented blocks for supporting a first body of fluid to be pressurized to a predetermined level,

means for supplying a compressional axial and tangential support stresses to said array such that when said fluid is pressurized to said predetermined level the working stress across at least a portion of said array is a predetermined ratio of the fatigue stress of the material of which said blocks are made;

a multiring assembly including a plurality of press fitted rings for supporting a second body of fluid to be pressurized to a predetermined level,

Delta said rings having radial interferences at the inner radii thereof such that when said second body of fluid is pressurized to said predetermined level, the working stresses at said inner radii are substantially equal to each other and substantially equal to the fatigue stress of the material of which said rings are made.

21. A pressure vessel, comprising:

an array of radially disposed segmented blocks for supporting a body of operating fluid to be contained within such vessel and to be pressurized to a predetermined level;

a multiring assembly including a plurality of press fitted rings for supporting a body of support fluid to be received within said vessel and to be pressurized to a predetermined level, said support fluid for supplying compressional tangential support stress to said array; and

means for supplying compressional axial support stress to said array;

said axial and tangential support stresses being of predetermined magnitudes such that when said operating fluid is pressurized to said predetermined level the working stress across at least a portion of said array is a predetermined ratio of the fatigue stress of the material of which said blocks are made;

said plurality of press fitted rings having radial interferences between the inner radii thereof of predetermined magnitudes such that when said body of support fluid is pressurized to said predetermined level the working stresses at said inner radii are substantially equal to each other and substantially equal to the fatigue stress of the material of which said rings are made.

22. A pressure vessel, comprising:

a central chamber for receiving a body of operating fluid to be pressurized to a predetermined level;

an array of radially disposed segmented blocks for supporting said central chamber;

means for supplying compressional axial support stress to at least a portion of said array;

an outer annular chamber for receiving a body of support fluid to be pressurized to a predetermined level;

when said operating fluid and said support fluid are pressurized to their respective predetermined levels, said sup port fluid supplies compressional tangential support stress to said array and cooperates with said axial support means to maintain the working stress across at least a por' tion of said array at a level substantially equal to the fatigue stress of the material of which said segmented blocks are made; and

a multiring assembly including a plurality of press fitted rings for supporting said annular chamber, said rings having radial interferences at the inner radii thereof such that, when said support fluid is pressurized to its predetermined level, the working stresses at the inner radn are substantially equal and substantially equal to the fatigue stress of the material of which said rings are made.

23. A pressure vessel for containing a fluid to be pressurized to a predetermined operating level, comprising:

an array of radially disposed segmented blocks for supporting said fluid and which experience working stress upon said fluid being pressurized to said predetermined operating level;

means for applying variable compressional axial support stress to said array;

means for applying variable compressional tangential support stress to said array; said support stresses being of predetermined values for making said working stress across at least a portion of said array a predetermined ratio of the fatigue stress of the material of which said segmented blocks are made; and

said means for applying variable compressional axial sup port stress being operable independently of said means for applying compressional tangential support stress.

24. A pressure vessel according to claim 23 wherein said predetermined ratio is substantially equal to the fatigue stress of the material of which said segmented blocks are made.

25. A pressure vessel according to claim 23 wherein said predetermined ratio is such that said working stress is less than the fatigue stress of the material of which said segmented blocks are made.

26. A pressure vessel according to claim 23 wherein said compressional axial support stress is provided by opposed pistons engageable with at least a portion of said array.

27. A pressure vessel according to claim 23 wherein said compressional tangential support stress is provided by a body of pressurized support fluid to be contained in an annular pressure chamber concentrically surrounding said array.

28. A pressure vessel according to claim 23 wherein said array is surrounded by a chamber for receiving a body of pressurized support fluid for providing said compressional tangential support stress.

UNTTED STATES PATENT OFFICE CERTiFICATE OF CORRECTION Patent No. 3 i 635 a 616 D d January 18 1972 Inventor) PERUVEMBA. SWAMINATHA it is certified that-error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

T No, [72] Inventor: St/ral ninathan should read --Swaminatha Column 1, line 53, after "of" insert a--. \J Column 2, line 31, "lever" should read --level--.

Column 6 line 31, ro" should read -or--. Column 8, Equation 12, should read Column 8, line 67, radii" should read --radial-- Column 9, Equation 1 lines 19 and 20, should read 2 S R l R Column 9, Equation 15, lines #3 and 44, should read 2 2 \y S R1 1 (l R Tn-l no load l (continued next page) J PAGE 2.

i TED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 5, 35, Dated January 97 Inventor(s) PERUVEMBA. SWAMINATHA. VENKATESAN It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 10 Equation 17, lines 7 and 8, should read 3 2 2 Delta Rn-l interf n--l n l E (R 2 R 2 R 2 R 2 n-l l n n-l v Column lO,'line ll, "Delta'n should read --Delta Column 13, claim 19, lines 7 and 8, should read 2 2 2 2 n-l 1 n n-l Column 13, claim 20, line l L, delete "a" Signed and sealed this 27th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

1. A pressure vessel for containing a fluid to be pressurized to a predetermined level, comprising: an array of radially disposed segmented blocks for supporting said fluid; and means for supplying compressional axial and tangential support stresses to said array such that when said fluid is pressurized to said predetermined level the working stress across at least a portion of said array is a predetermined ratio of the fatigue stress of the material of which said blocks are made.
 2. A pressure vessel according to claim 1 wherein said predetermined ratio is such that said working stress is substantially equal to the fatigue stress of the material of which said blocks are made.
 3. A pressure vessel according to claim 1 wherein said predetermined ratio is such that said working stress is less than the fatigue stress of the material of which said segmented blocks are made.
 4. A pressure vessel for containing a fluid to be pressurized to a predetermined level, comprising: an array of radially disposed segmented blocks for supporting said fluid; means for supplying compressional axial support stress to said array; and means for supplying compressional tangential support stress to said array, said applied support stresses being of predetermined values such that when said fluid is pressurized to said predetermined level, the working stress across said array does not exceed the fatigue stress of the material of which said blocks are made.
 5. A pressure vessel for containing a fluid to be pressurized to a predetermined operating level, comprising: an array of radially disposed segmented blocks for supporting said fluid and which experience working stress upon said fluid being pressurized to said predetermined operating level; means for applying compressional axial support stress to said array; and means for applying compressional tangential support stress to said array, said support stresses being of predetermined values for making said working stress across at least a portion of said array a predetermined ratio of the fatigue stress of the material of which said segmented blocks are made.
 6. A pressure vessel according to claim 5 wherein said predetermined ratio is substantially equal to the fatigue stress of the material of which said segmented blocks are made.
 7. A pressure vessel according to claim 5 wherein said predetermined ratio is such that said working stress is less than the fatigue stress of the material of which said segmented blocks are made.
 8. A pressure vessel according to claim 5 wherein said compressional axial support stress is provided by opposed pistons engageabLe with at least a portion of said array.
 9. A pressure vessel according to claim 5 wherein said compressional tangential support stress is provided by a body of pressurized support fluid to be contained in an annular pressure chamber concentrically surrounding said array.
 10. A pressure vessel according to claim 5 wherein said array is surrounded by a chamber for receiving a body of pressurized support fluid for providing said compressional tangential support stress.
 11. In a pressure vessel including a central chamber for containing a body of operating fluid to be pressurized to a predetermined operating level Po , the improvement comprising: an array of radially disposed segmented blocks surrounding and supporting the chamber, said blocks experiencing working stress Sw upon said operating fluid being pressurized to said operating level Po ; and means for supplying compressional axial Sa and tangential St support stresses to said array such that when said operating fluid is pressurized to said predetermined operating level Po , the working stress Sw across at least a portion of said array is a predetermined ratio of the fatigue stress of the material of which said segmented blocks are made.
 12. In a pressure vessel the combination according to claim 11 wherein said compressional axial Sa and tangential St support stresses at the bore of said central chamber are substantially equal to the operating fluid pressure Po of said operating fluid minus the fatigue stress Sf of the material of which said segmented blocks are made.
 13. In a pressure vessel the combination according to claim 11 wherein said compressional axial and tangential support stresses applied to said array are average compressional support stresses substantially equal to ((Dw-D1) (Po-Sw/2)).
 14. A pressure vessel for containing a body of fluid to be pressurized to a predetermined level; comprising: a multiring assembly including a plurality of rings for supporting said fluid, said rings being provided with radial interferences such that when said fluid is pressurized to said predetermined level the working stress at each radius, except the outermost, is a predetermined ratio of the fatigue stress of the material of which the rings are made.
 15. A pressure vessel according to claim 14 wherein said predetermined ratio is such that said working stress is equal to the fatigue stress of the material of which said rings are made.
 16. A pressure vessel according to claim 14 wherein said predetermined ratio is such that said working stress is less than the fatigue stress of the material of which rings are made.
 17. A pressure vessel for containing a body of fluid to be pressurized to a predetermined level, comprising: a multiring assembly including a plurality of rings for supporting said fluid; said rings fitted together and having radial interferences at the inner radii thereof; and said interferences being such that, when said fluid is pressurized to said predetermined level, said radial interferences are such that the working stress at said inner radii are equal to each other and equal to the fatigue stress of the material of which said rings are made.
 18. A pressure vessel for containing a body of fluid to be pressurized to a predetermined level, comprising: a multiring assembly including a plurality of rings for supporting said fluid; said rings being press fitted together and having radial interferences at the inner radii thereof; and said interferences being such that, when said fluid is pressurized to said predetermined level, said stress at said inner radii are substantially equal to each other and less than the fatigue stress of the material of which said rings are made.
 19. A pressure vessel for containing a body of fluid to be pressurized to a predetermined level, comprising: a multiring assembly including a plurality of rings for supporting said fluid; said rings being press fitted together and having radial interferences at the inner radii thereof; and said interferences being such that when said fluid is pressurized to said predetermined level, the stresses experienced by said assembly at said inner radii are defined by:
 20. A pressure vessel, comprising: an array of radially disposed segmented blocks for supporting a first body of fluid to be pressurized to a predetermined level, means for supplying a compressional axial and tangential support stresses to said array such that when said fluid is pressurized to said predetermined level the working stress across at least a portion of said array is a predetermined ratio of the fatigue stress of the material of which said blocks are made; a multiring assembly including a plurality of press fitted rings for supporting a second body of fluid to be pressurized to a predetermined level, said rings having radial interferences at the inner radii thereof such that when said second body of fluid is pressurized to said predetermined level, the working stresses at said inner radii are substantially equal to each other and substantially equal to the fatigue stress of the material of which said rings are made.
 21. A pressure vessel, comprising: an array of radially disposed segmented blocks for supporting a body of operating fluid to be contained within such vessel and to be pressurized to a predetermined level; a multiring assembly including a plurality of press fitted rings for supporting a body of support fluid to be received within said vessel and to be pressurized to a predetermined level, said support fluid for supplying compressional tangential support stress to said array; and means for supplying compressional axial support stress to said array; said axial and tangential support stresses being of predetermined magnitudes such that when said operating fluid is pressurized to said predetermined level the working stress across at least a portion of said array is a predetermined ratio of the fatigue stress of the material of which said blocks are made; said plurality of press fitted rings having radial interferences between the inner radii thereof of predetermined magnitudes such that when said body of support fluid is pressurized to said predetermined level the working stresses at said inner radii are substantially equal to each other and substantially equal to the fatigue stress of the material of which said rings are made.
 22. A pressure vessel, comprising: a central chamber for receiving a body of operating fluid to be pressurized to a predetermined level; an array of radially disposed segmented blocks for supporting said central chamber; means for supplying compressional axial support stress to at least a portion of said array; an outer annular chamber for receiving a body of support fluid to be pressurized to a predetermined level; when said operating fluid and said support fluid are pressurized to their respective predetermined levels, said support fluid supplies compressional tangential support stress to said array and cooperates with said axial support means to maintain the working stress across at least a portion of said array at a level substantially equal to the fatigue stress of the material of which said segmented blocks are made; and a multiring assembly including a plurality of press fitted rings for supporting said annular chamber, said rings having radial interferences at the inner radii thereof such that, when said support fluid is pressurized to its predetermined level, the working stresses at the inner radii are substantially equal and substantially equal to the fatigue stress of the material of which said rings are made.
 23. A pressure vessel for containing a fluid to be pressurized to a predetermined operating Level, comprising: an array of radially disposed segmented blocks for supporting said fluid and which experience working stress upon said fluid being pressurized to said predetermined operating level; means for applying variable compressional axial support stress to said array; means for applying variable compressional tangential support stress to said array; said support stresses being of predetermined values for making said working stress across at least a portion of said array a predetermined ratio of the fatigue stress of the material of which said segmented blocks are made; and said means for applying variable compressional axial support stress being operable independently of said means for applying compressional tangential support stress.
 24. A pressure vessel according to claim 23 wherein said predetermined ratio is substantially equal to the fatigue stress of the material of which said segmented blocks are made.
 25. A pressure vessel according to claim 23 wherein said predetermined ratio is such that said working stress is less than the fatigue stress of the material of which said segmented blocks are made.
 26. A pressure vessel according to claim 23 wherein said compressional axial support stress is provided by opposed pistons engageable with at least a portion of said array.
 27. A pressure vessel according to claim 23 wherein said compressional tangential support stress is provided by a body of pressurized support fluid to be contained in an annular pressure chamber concentrically surrounding said array.
 28. A pressure vessel according to claim 23 wherein said array is surrounded by a chamber for receiving a body of pressurized support fluid for providing said compressional tangential support stress. 